Cool! Thanks for the input. We did hit it bigtime with sequestering agent (assuming that products called "Pool Magnet" and "Metal Free" fit that category--- over about a week we put in around 4 liters of Pool Magnet, and I think 10 liters of Metal Free.). They helped us get the iron down from around 6-7 ppm down under .2ppm. Copper tested at nothing, and we had our refill water tested and found that iron is not a problem, though that well does show 500 ppm phosphates, so we'll have to keep an eye on that once we manage to get the levels down this time.

So we're going to go with the strong bleach chlorination, checking levels a few times a day to keep it there, and running the filter 24/7, (we're also now adding DE to the filter after each backwash). (The remaining alum in the water won't cause longterm problems for the sand filter, will it?)

And yes, we'll be getting drop test kits soon. So far, most of the test readings are coming from repeated testing at the actual pool shop, where they are doing all the drop tests.

Thanks so much for the reply!